1. Field of the Invention
The present invention relates to the field of internal combustion engine control and more specifically to a system for detecting the use of a block heater device and providing a modified variable for such control.
2. Disclosure Information
In cold climates, block heater devices are often used to heat the coolant fluid in the blocks of internal combustion engines. Such heaters are well known and are useful in lowering the viscosity of oil and coolant fluids while engines are turned off, in order to reduce the power requirements necessary to start the engines in extremely cold conditions.
When a block heater is in use, the distribution of heat throughout the coolant is uneven and the temperatures vary widely during the time the engine is not operating. A problem identified in the use of block heaters is that an engine coolant temperature sensor (ECT), because of its close proximity to the block heater element and the non-circulating but heated coolant, can provide a higher temperature reading at initial cold start-up than the actual average or distributed temperature of the coolant. When this occurs, the engine control system receives false or inaccurate information and may provide a leaner air/fuel mixture than the engine can effectively use to achieve a start. The problem may persist for approximately the first half-minute following the commencement of the start cycle, until the coolant is pumped and circulated within the engine block and the sensor reads the proper temperature of the coolant.
The problem of inaccurate coolant temperature readings during the cold start cycle, due to the usage of an engine block heater, is recognized in commonly assigned U.S. Pat. No. 5,781,877 to Rachel, et al, which is hereby incorporated by reference into this application.
In U.S. Pat. No. 5,781,877, the solution involves the use of component sensors that are already part of the engine control system, including an ambient air temperature sensor, a heated exhaust gas oxygen sensor (HEGO) and an engine coolant temperature sensor. If the temperature measurements at start up for each of the three sensors are below predetermined levels, indicating extremely low temperatures, a determination is made that there is a possibility that a block heater is in use. Once that determination is made, the disclosed method calculates a delta temperature value that serves to offset and lower the value provided by the engine coolant sensor to the engine control system. The modified temperature value is then used by the engine control system as a substitute for the output of the engine coolant sensor in providing calculations of proper component levels of air/fuel mixture. The use of the calculated delta offset continues until the HEGO sensor reaches a predetermined level to indicate that the engine has started and is running, or until the coolant temperature reaches a predetermined level.
The present invention has the advantage of relying on the output of only two sensors and therefore performing fewer steps in the process than the prior art. In addition, the process for compensating for the effects of the block heater usage on the engine coolant temperature sensor provides a highly accurate and changing normalized value of coolant temperature variable to the engine control system.
The process is performed following a key-on start command, by initially measuring the ambient air temperature to determine whether the air is cold enough to make a difference in the start sequence of the engine control system. If the air temperature is indeed below a defined extreme cold threshold value, the process continues and calculates the difference between the sensed engine coolant temperature and an inferred engine coolant temperature. If the difference is greater than a predetermined amount, it is determined that the output of the engine coolant temperature sensor has been effected enough by the heater to adversely influence the calculations of the engine control system as it attempts to provide the proper air/fuel mixture for starting the engine in extreme cold. A normalized engine coolant temperature value is then determined and that value is initially provided to the engine control system as a substitute for the temperature value output by the engine coolant temperature sensor. As the engine is then cranked and begins to operate the water/coolant pump to circulate the coolant fluid within the engine block, the normalized engine coolant temperature value is recalculated with each cycle of the program and filtered in a way that it approaches the actual value provided by the engine coolant temperature sensor within the first half minute during a continuous start process.
The present invention has been optimized to account for the gradual transition in engine coolant temperature from a non-uniform distribution to a more uniform distribution as the engine begins turning and the engine coolant is circulated and mixed. The method is also designed to correctly account for repeated key-on and key-off cycling, restarts after stalls, short engine soaks or short engine running periods. Such enhancements provide for much improved engine start and run fuel delivery during all block heater assisted starts.
It is therefore an object of the present invention to provide an enhancement to an engine control system that overcomes the effects of inaccurate coolant temperature readings when a block heater is being used in cold weather conditions.
It is another object of the present invention to provide a highly accurate compensation to the inaccurate coolant temperature sensor reading until there is sufficient coolant circulation in the engine to allow the system to rely on the sensor""s readings.
These advantages and objects of the present invention, as well as others, will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.